The role of lithium in hydrogen trapping and embrittlement of Al-Cu-Li alloys: Experimental study and DFT calculations

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The role of lithium in hydrogen embrittlement (HE) and trapping of Al-Cu-Li alloys were investigated in experimental and density functional theory (DFT) calculations. The tensile curves and fracture morphology show that the Li-contained samples are more sensitive to HE than the Li-free samples and the HE sensitivity increases with the aging time expansion. The Transmission Electron Microscope (TEM) analyses reveal that the number density of T1 (Al2CuLi) precipitates increases about 66.8% with aging process, suggesting that HE sensitivity is exacerbated by T1 precipitates. In addition, the lithium in T1 precipitates, solid solution matrix and solute segregation grain boundaries (GBs) always has a high affinity to hydrogen according to DFT calculations, where T1 precipitates have the highest hydrogen trapping energy with 0.736 eV/H atom. Moreover, the influence of hydrogen on Al-Cu-Li alloys was investigated using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and electrochemical corrosion analysis. These analyses indicate that hydrogen exists in the form of hydrogen atoms, which results in a reduction in corrosion potential (Ecorr) from −676.3 mV to −699.3 mV by approximately 20 mV and an increase in corrosion current density (icorr) from 2.1×10−6 A/cm2 to 10.8×10−6 A/cm2 by an order of magnitude. The accumulated hydrogen atoms eventually lead to corrosion pits and blisters on the surface of alloys.